Geothermal wells have been drilled in the past to recover the internal earth heat by producing the steam resulting therefrom. Usually such wells have included a casing head at the surface which is surmounted by an expansion spool, one or more master control valves and when needed a lubricator connected at the top of the structure which allows the introduction of elements into the well bore through the lubricator without sacrificing the pressurized steam production.
Such geothermal wells have included a tubing string run through the interior of the casing. Such tubing string can be used for start-up of the well, for control, for corrosion control, for testing and for scaling control or other purposes. Prior to the present invention different means have been used for the introduction of a tubing string into the casing head or expansion spool and into the casing of a geothermal well. One such means has included an angled connection into the upper portion of the expansion spool or spool adapter which is oriented at a slight angle to the vertical so that a coil of tubing can be run in a manner similar to a wireline into the casing. Insertion of the coiled tubing into the casing involves substantial expense not only for the special coiled tubing but for the highly specialized equipment and services required to uncoil and insert the tubing. Such equipment and services is offered by several companies such as Bowen Tools, Inc. of Houston, Tex. Bowen's coiled tubing units are shown and described on pages 541 through 544 of the 1990-91 edition of the Composite Catalogue of Oil Field Equipment and Services (by Gulf Publishing Company, Houston, Tex.). Another disadvantage that geothermal well operators face because of coiled tubing is the increased height of the production tree due to the angled connection member. Also, the use of coiled tubing requires that the master control valve/valves be located below the angled connection member. This requires the use of expensive master valves with the capability of shearing the coiled tubing and sealing in an emergency.
U.S. Pat. No. 4,390,063 discloses a particular annular packing for a geothermal well which packing is used to seal the annulus surrounding the inner production casing. The well structure includes the well casing the inner production casing within the expansion spool, a master valve and other flow and control structures. There is no suggestion that there be a tubing string extending into the well casing with the improved hanger spool structure of the present invention.
U.S. Pat. No. 3,976,130 discloses a geothermal well together with a packing structure. There is no suggestion of any of the improved structures of the present invention. U.S. Pat. No. 4,512,410 discloses a geothermal expansion wellhead system. There is no suggestion in this reference of any of the improved structures of the present invention.